The present invention relates to a variable focus lens for use in image reproduction, and more particularly to a variable focus lens for use in copying images, platemaking, or the like, the lens being capable of continuously varying the magnification while keeping a finite object-to-image distance constant.
Copying machines and printers mostly use an equal-size magnification ratio (i.e., no size enlargement or reduction) for copying images and platemaking. However, more and more copying machines and printers are required to have a size enlarging and reducing function. To meet such a requirement, there is a demand for a variable focus lens capable of continuously varying the magnification while keeping a finite object-to-image distance constant.
Variable focus lenses which can vary the magnification without varying the entire length of the lenses are compact and suitable for smaller F values. The lenses of this type vary the magnification by moving internal lens elements thereof. The lenses of this class are disclosed in Japanese Laid-Open Patent Publications Nos. 48-49453, 53-60655, 57-67909, 59-61814, 60-121414, 61-151604, 61-198205, and 62-123421, for example.
The conventional lenses have however proven unsatisfactory in that their magnification range is small, they have large F numbers, and cannot have an aperture efficiency of 100%.